Aftermarket Speedometer Calibration
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Joined: Feb 2014
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From: Seattle
Aftermarket Speedometer Calibration
I have installed an aftermarket speedometer in my 1969 F-100 4X4 with a 4 speed manual transmission using the existing speedometer cable. The existing cable appeared to be working (bouncing between 30MPH and 40MPH when traveling at 35MPH) but the new speedometer shows about 20 MPH when we are traveling at about 35 MPH. The manufacture of the speedometer states that the spedometer is designed for a 1:1 drive ratio (60 MPH @ 1000 RPM) and that the pinion gear may need to be changed to acheive to correct reading. I have searched the forum to find what my current cable drive ratio is but couldnt find any posts. Do I need to change my pinion gear, or could I have a bad speedometer cable that simply needs to be replaced?
Mike and Dane
Mike and Dane
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Joined: Mar 2013
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From: Phoenix, Az.
IMHO you ought to start with the cable. Beings it was bouncing before I am assuming the cable is worn out. Most times lubing it is a temporary fix since the cable core wears in to the inside of the housing usually. I always suggest fixing what you know is broke 1st. Then move on. The driven speedo gear on the end of the cable is probably still available from Ford. Each tooth on it is a 3-5 MPH change at the speedo. If your speedo says 20 MPH when you are going 35 MPH then I would buy a speedo gear with 4 teeth less than your current gear has. Ford makes 16 through 21 tooth gears. If that means you need less than 16 teeth then you have to change the speedo drive gear in the tranny.
Fleet Mechanic
Joined: May 2001
Posts: 1,396
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From: Cupertino
Change the rearend to correct the speedometer? Methinks you should reinstall the old speedometer and sent the new one back to the manufacturer for placement where the sun doesn't shine along with his advice.
We are good at correcting your problem on old stock Ford trucks.
We are good at correcting your problem on old stock Ford trucks.
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From: Seattle
Maybe I should restate the question. I am wondering if anyone knows if the stock speedometer cable is rotating at a 1:1 ratio or 1000 RPMs showing 60 MPH on the stock speedometer. If this is not the case I need to change the pinion gear which drives the speedometer cable (not the pinion gear in the differential).
Cargo Master
Joined: Apr 2009
Posts: 3,038
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From: South west Idaho
I suggest replacing the cable and probably worn out cable housing first . Then if it is smooth but not correct , change the driven gear . Forget about the pinion gear , that's why different different speedometer gears are made , to correct speedometers. Why make something simple hard to do ?
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Joined: Mar 2013
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From: Phoenix, Az.
I suggest replacing the cable and probably worn out cable housing first . Then if it is smooth but not correct , change the driven gear . Forget about the pinion gear , that's why different different speedometer gears are made , to correct speedometers. Why make something simple hard to do ?
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Joined: Oct 2012
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From: Aviston, Il
I think when the OP said he needed to change the pinion gear, he was referring to the driven speedometer gear, not the ring and pinion gears in the rear end. Technically, it is also a pinion gear, and that may have been what the speedometer manufacturer called it when he spoke to them.
Like Jeff stated before, make sure your cable is good first or replace it. Then count the teeth on your speedometer gears. After that, its simple math to figure out which speedometer gears that you need to correctly adjust. Or if you are not so good with numbers, there are plenty of online speedometer gear calculators to help you figure out what you need.
Like Jeff stated before, make sure your cable is good first or replace it. Then count the teeth on your speedometer gears. After that, its simple math to figure out which speedometer gears that you need to correctly adjust. Or if you are not so good with numbers, there are plenty of online speedometer gear calculators to help you figure out what you need.
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Joined: Aug 2003
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From: **** hole San Jose ca.
It may have the steel gears at the speedometer gear out put. If so not cheap to replace those type. If you can find them in the right number of teeth count you need..
Maybe you should have gone with a electric one easier to setup.
But cost a little more as you can recalibrate if you change tire sizes it's no big deal
where as you'd have to change gear teeth again..
orich
Maybe you should have gone with a electric one easier to setup.
But cost a little more as you can recalibrate if you change tire sizes it's no big deal
where as you'd have to change gear teeth again..
orich
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Joined: Mar 2013
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From: Phoenix, Az.
Or you can buy an adaptor that goes on the end of the cable to change the ratio and dial in the speedo.
Dick's Speed-O-Tach
4325 N. 7th Street
Phoenix , Az 85014
(602) 279-6463
FAX (602) 285-0817
dicksspeedotach@yahoo.com
ODOMETERS SPEEDOMETER ~ ODOMETER RESET / MILEAGE SET WITH VALIDATION ~ DIGITAL / ANALOG REPAIRS
~ PIXEL REPAIR ON DARK OR PARTIALLY LIT DISPLAYS ~ MECHANICAL SPEEDOMETER
~ DIGITAL INFORMATION CENTER REPAIRS, VDO,LCDS ~ ELECTRONIC SPEEDOMETER
~ ANALOG & DIGITAL ODOMETER ~ REBUILD SPEEDOMETER
~ SPEEDOMETER REPLACEMENT
SPEEDOMETER CABLES SPEED TESTING
~ CUSTOM REPLACEMENT CABLES ~ IN - SHOP DYNAMOMETER
~ CABLE INSTALLATIONS ~ CERTIFIED CALIBRATIONS
~ KEYS & ENDS FITTED ~ ELECTRONIC RATIO ADAPTER
~ MECHANICAL RATIO ADAPTERS ~ BENCH TESTING
TACHOMETER CABLES / RPM GAS/TEMP/ETC.
~ ELECTRONIC TACHOMETER REPAIR ~ GAS,TEMP,OIL REPAIR
~ TACHOMETER CALIBRATIONS ~ ANTIQUE MECHANIC CLOCKS
~ ANTIQUE CONVERSION 6V / 12V ~ ELECTRONIC CLOCK REPAIR
~ REBUILD TACHOMETER ~ LEXUS SC,GS,ES NEEDLES
PROVIDING THE BEST GAUGE SERVICE IN ARIZONA SINCE 1961
4325 N. 7th Street
Phoenix , Az 85014
(602) 279-6463
FAX (602) 285-0817
dicksspeedotach@yahoo.com
ODOMETERS SPEEDOMETER ~ ODOMETER RESET / MILEAGE SET WITH VALIDATION ~ DIGITAL / ANALOG REPAIRS
~ PIXEL REPAIR ON DARK OR PARTIALLY LIT DISPLAYS ~ MECHANICAL SPEEDOMETER
~ DIGITAL INFORMATION CENTER REPAIRS, VDO,LCDS ~ ELECTRONIC SPEEDOMETER
~ ANALOG & DIGITAL ODOMETER ~ REBUILD SPEEDOMETER
~ SPEEDOMETER REPLACEMENT
SPEEDOMETER CABLES SPEED TESTING
~ CUSTOM REPLACEMENT CABLES ~ IN - SHOP DYNAMOMETER
~ CABLE INSTALLATIONS ~ CERTIFIED CALIBRATIONS
~ KEYS & ENDS FITTED ~ ELECTRONIC RATIO ADAPTER
~ MECHANICAL RATIO ADAPTERS ~ BENCH TESTING
TACHOMETER CABLES / RPM GAS/TEMP/ETC.
~ ELECTRONIC TACHOMETER REPAIR ~ GAS,TEMP,OIL REPAIR
~ TACHOMETER CALIBRATIONS ~ ANTIQUE MECHANIC CLOCKS
~ ANTIQUE CONVERSION 6V / 12V ~ ELECTRONIC CLOCK REPAIR
~ REBUILD TACHOMETER ~ LEXUS SC,GS,ES NEEDLES
PROVIDING THE BEST GAUGE SERVICE IN ARIZONA SINCE 1961
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